In recent years, requirements for realization of high-processing speed in electrical equipment have been increasing. With the requirements, it has been desired to realize a high-transmission speed of electrical signals in an electric circuit board installed in the electrical equipment. Under this background, transmission through optical signals has been conceived as means for overcoming the limit of the transmission speed of electrical signals. Various photoelectric hybrid substrates in which an electric circuit board and an optical waveguide are hybridized have been proposed.
An example of such a photoelectric hybrid substrate that has been proposed is a photoelectric hybrid substrate which includes a substrate and an optical waveguide stacked on the substrate, the optical waveguide including a lower cladding layer, a core layer, and an upper cladding layer that are sequentially formed on the substrate so as to be parallel to the substrate (for example, Japanese Unexamined Patent Application Publication No. 2004-325636). In this photoelectric hybrid substrate, an electrical signal is transmitted through electrical wiring provided on a surface of the substrate, and an optical signal is transmitted by reflecting the optical signal at an interface between the core layer and the cladding layer that form the optical waveguide.